The objective is to define the molecular basis of sperm-egg interactions during fertilization. The experiments focus on the structure and function of four fertilization proteins, lysin, 18K, VERL and ADP ribosyl cyclase, and on the cyclase homologue, CD38. The Specific Aims address the structural basis of species specificity and the mechanisms of dissolution of the egg VE, fusion of the sperm and egg membranes, and synthesis of cADPR. Two abundant gamete recognition proteins from the abalone sperm are lysin and the 18K protein. Lysin hypervariable residues mediate recognition of the egg vitelline envelope (VE) receptor for lysin (VERL). Lysin binds irreversibly to the VERL resulting in non-enzymatic dissolution of the VE. The 18K protein mediates fusion of the gamete plasma membranes. The goals are to solve and analyze crystal structures of monomeric and dimeric lysin and the 18K protein from two abalone species, and to crystallize the lysin:VERL complex. These experiments will establish the structural basis of species specificity residing in lysins from divergent species, visualize the interaction of lysin with the VERL, and define the structure and function of the 18K protein.
General Significance How does the specific recognition, binding and fusion of sperm and egg cells occur? Although a great deal is being learned about cellular processes, very little is known about the molecular interactions that underlie the process of fertilization. Sperm-egg interaction remains one of the least understood fundamental biological processes, and yet it is exemplary of the general problem of how cells use surface molecules to adhere to each other and intercommunicate. Marine invertebrates have long been used as model systems to study basic biological processes. Abalone are advantageous model organisms in which to study fertilization biochemically. Key events during sperm-egg interaction in abalone are species specific binding of the gametes, dissolution of the egg protective coat and fusion of sperm and egg membranes. Proteins involved in these key steps of fertilization will be studied to determine their structure and function.
